linux-kernel - Re: [PATCH] KVM: SVM: delay svm_vcpu_init

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Date:   Tue, 27 Jul 2021 17:23:29 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Dan Carpenter <dan.carpenter@...cle.com>,
        Vineeth Pillai <viremana@...ux.microsoft.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH] KVM: SVM: delay svm_vcpu_init_msrpm after svm->vmcb is
 initialized

Paolo Bonzini <pbonzini@...hat.com> writes:

> Right now, svm_hv_vmcb_dirty_nested_enlightenments has an incorrect
> dereference of vmcb->control.reserved_sw before the vmcb is checked
> for being non-NULL.  The compiler is usually sinking the dereference
> after the check; instead of doing this ourselves in the source,
> ensure that svm_hv_vmcb_dirty_nested_enlightenments is only called
> with a non-NULL VMCB.
>
> Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
> Cc: Vineeth Pillai <viremana@...ux.microsoft.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> [Untested for now due to issues with my AMD machine. - Paolo]

At least this doesn't seem to break kvm-amd on bare metal, so

Tested-by: Vitaly Kuznetsov <vkuznets@...hat.com>

> ---
>  arch/x86/kvm/svm/svm.c          | 4 ++--
>  arch/x86/kvm/svm/svm_onhyperv.h | 2 +-
>  2 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 9a6987549e1b..4bcb95bb8ed7 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -1406,8 +1406,6 @@ static int svm_create_vcpu(struct kvm_vcpu *vcpu)
>  		goto error_free_vmsa_page;
>  	}
>  
> -	svm_vcpu_init_msrpm(vcpu, svm->msrpm);
> -
>  	svm->vmcb01.ptr = page_address(vmcb01_page);
>  	svm->vmcb01.pa = __sme_set(page_to_pfn(vmcb01_page) << PAGE_SHIFT);
>  
> @@ -1419,6 +1417,8 @@ static int svm_create_vcpu(struct kvm_vcpu *vcpu)
>  	svm_switch_vmcb(svm, &svm->vmcb01);
>  	init_vmcb(vcpu);
>  
> +	svm_vcpu_init_msrpm(vcpu, svm->msrpm);
> +
>  	svm_init_osvw(vcpu);
>  	vcpu->arch.microcode_version = 0x01000065;
>  
> diff --git a/arch/x86/kvm/svm/svm_onhyperv.h b/arch/x86/kvm/svm/svm_onhyperv.h
> index 9b9a55abc29f..c53b8bf8d013 100644
> --- a/arch/x86/kvm/svm/svm_onhyperv.h
> +++ b/arch/x86/kvm/svm/svm_onhyperv.h
> @@ -89,7 +89,7 @@ static inline void svm_hv_vmcb_dirty_nested_enlightenments(
>  	 * as we mark it dirty unconditionally towards end of vcpu
>  	 * init phase.
>  	 */
> -	if (vmcb && vmcb_is_clean(vmcb, VMCB_HV_NESTED_ENLIGHTENMENTS) &&
> +	if (vmcb_is_clean(vmcb, VMCB_HV_NESTED_ENLIGHTENMENTS) &&
>  	    hve->hv_enlightenments_control.msr_bitmap)
>  		vmcb_mark_dirty(vmcb, VMCB_HV_NESTED_ENLIGHTENMENTS);
>  }

-- 
Vitaly